1. Field of the Invention
This invention relates to a radiation image read-out apparatus and a stimulating light cut filter for the radiation image read-out apparatus, and more particularly to a radiation image read-out apparatus in which stimulated emission emitted from a radiation image convertor panel upon exposure to stimulating light is detected and to a stimulating light cut filter which transmits the stimulated emission but cuts the stimulating light.
2. Description of the Related Art
When certain kinds of phosphor are exposed to radiation such as X-rays, they store a part of energy of the radiation. Then when the phosphor which has been exposed to the radiation is exposed to stimulating light such as visible light, light is emitted from the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is generally referred to as “a stimulable phosphor”. In this specification, the light emitted from the stimulable phosphor upon stimulation thereof will be referred to as “stimulated emission”. There has been known a radiation image recording and reproducing system, comprising a radiation image recording apparatus and a radiation image read-out apparatus, as a CR (computed radiography) in which a layer of the stimulable phosphor is exposed to a radiation passing through an object such as a human body to have a radiation image of the object stored on the stimulable phosphor sheet as a latent image, stimulating light such as a laser beam is projected onto the stimulable phosphor sheet, and the stimulated emission emitted from the stimulable phosphor sheet is photoelectrically detected, thereby obtaining an image signal (a radiation image signal) representing a radiation image of the object. There has been known a radiation image convertor panel comprising a stimulable phosphor layer formed on a substrate as a recording medium employed in the radiation image recording and reproducing system.
As the radiation image read-out apparatus, there has been known an apparatus comprising a detecting means which detects stimulated emission emitted from a radiation image convertor panel upon exposure to a line-like stimulating light beam extending in a main scanning direction and a stimulating light cut filter which is disposed between the radiation image convertor panel and the detecting means. The stimulating light cut filter is formed of, for instance, colored glass and transmits the stimulated emission but cuts the stimulating light. See, for instance, U.S. Pat. Nos. 6,479,835, 6,495,850, 6,501,088, 6,504,169, 6,512,240 and 6,528,812.
There has been a demand for shortening the space between the radiation image convertor panel and the detecting means in order to reduce the overall size of the apparatus. Especially in the case of an apparatus comprising a detecting means which detects the stimulated emission by way of an imaging optical system, the resolution can be increased by increasing the numerical aperture (NA) of the imaging optical system by bringing the detecting means nearer to the radiation image convertor panel. The detecting means can be brought nearer to the radiation image convertor panel by making thinner the stimulating light cut filter.
However, it has been difficult to make thinner the stimulating light cut filter without deteriorating the stimulating light cutting performance by improving the quality of the colored glass forming the stimulating light cut filter.